1. Field of the Invention
The present invention relates to an insulated wire for vehicle use and a cable for vehicle use and, in particular, the invention relates to an insulated wire for vehicle use and a cable for vehicle use each having flame retardance and having high oil resistance and an excellent low-temperature property (flexibility at low temperatures).
2. Description of the Related Art
Awareness of environmental issues has been growing worldwide, and there has been an increased demand for halogen-free materials which do not generate halogen gas at the time of combustion. Furthermore, in order to obtain high flame retardance by preventing flames from spreading at the time of a fire, it is necessary to add a large amount of a halogen-free flame retardant, such as a metal hydroxide (for example, refer to Japanese Unexamined Patent Application Publication No. 2010-97881).
However, addition of a large amount of a halogen-free flame retardant will degrade mechanical properties and also degrade a melt flow characteristic, thus limiting the range of usable forming machines.
On the other hand, insulated wires and cables used for vehicles, such as rolling stocks, automobiles, and robots, are required to have high oil resistance and a low-temperature property depending on the usage environment.
It is known that high oil resistance can be obtained by using polymers having high crystallinity or polymers having high polarity, and that a low-temperature property can be obtained by using materials having a low glass transition temperature (Tg).
However, in the case where polymers having high crystallinity are used in order to obtain high oil resistance, flexibility decreases, and wiring performance degrades when applied to insulated wires and cables.
Furthermore, a high VA content ethylene-vinyl acetate copolymer (EVA) having an acetic acid content (VA) of 50% by mass or more, which is an example of a polymer having high polarity, has excellent oil resistance while maintaining flexibility at normal temperature. However, it has a high Tg and a poor low-temperature property.